The present invention relates to preparation of a fuel blend for use in furnace-boiler units. More particularly, the invention relates to preparation of a fuel blend comprised of treated lignite and heavy hydrocarbon oil.
The use of a blend of solid carbonaceous material and liquid hydrocarbons as a fuel for furnace-boiler units, gas manufacture, metallurgical operations and other purposes is known in the art. U.S. Pat. No. 219,181 describes such a fuel blend. However, difficulties have been encountered in the use of such fuel blends due to separation of the solid fuel from the liquid.
An attempt to overcome the separation problem is described in U.S. Pat. No. 1,431,225, which suggests addition of an emulsifying agent to avoid settling of the powdered solid carbonaceous material.
U.S. Pat. No. 3,764,547 discloses a fuel slurry comprised of solid carbonaceous material in liquid hydrocarbon with addition of soot. Various improvements in solid-liquid fuel slurries are also described in U.S. Pat. Nos. 4,082,516; 4,090,853; 4,101,293; and 4,147,519.
A process for producing a low-sulpur fuel by heating low-grade coal followed by pulverizing it and blending it with oil is described in U.S. Pat. No. 3,932,145.
A process for upgrading lignite to increase its heating value is described in U.S. Pat. No. 4,052,168.
Thus, it can be seen that a great deal of work has been done in an effort to utilize solid carbonaceous material as a component in a furnace fuel. Two primary problems are encountered in trying to utilize lignite as a component in a blended fuel. When particulate lignite is added to liquid, it is generally necessary to use a stabilizing agent of some sort to prevent separation and settling of the solid particles. If a stabilizing agent is not used, physical stirring is required. This problem could be avoided by blending the solid material just prior to introducing it to a burner. However, this would require storage of the solid material for a significant period of time, and dried lignite is very suscepticle to spontaneous ignition, such that it is not practical to dry lignite and store it for extended periods of time prior to blending it with a liquid fuel.
The foregoing problems are overcome by the present invention.